1. Field of the Invention
The invention relates to a switched-mode power supply comprising a transformer provided with a primary winding having a first primary terminal, coupled to receive a voltage with respect to a ground terminal, and a second primary terminal; switching means coupled between the second primary terminal and the ground terminal; and a start-up circuit for starting up the switched-mode power supply, the start-up circuit comprising a field effect transistor of the normally-on type having a drain electrode coupled to the second primary terminal, a source electrode, and a gate electrode.
2. Description of the Related Art
Such a switched-mode power supply is known from European Patent Specification EP 0 585 788 A1. Said Specification describes a switched-mode power supply for use in an integrated circuit which does not require a separate IC terminal for supplying power to the start-up circuit. The start-up circuit is powered from the source of a junction field effect transistor, the junction field effect transistor being coupled in series between the switching means and the second primary terminal.